Systems and methods for code sequence extension over transmission in wireless communication environments

ABSTRACT

A transmitter for transmitting signals to a receiver is provided. The transmitter generates a padded code sequence comprising a plurality of symbols. The padded sequence is generated by padding the first symbol to the end of a code sequence. The padding method can be applied to Zadoff-Chu code, generalized chirp like code, CAZAC sequence to acquire extra code property, e.g. orthogonal in terms of differential detection. The padded code sequence can be allocated on sub-carriers of an OFDM symbol in frequency domain in increasing or decreasing order to resist linear phase shift due to time domain delay. If multiple OFDM symbols are used, the padded code sequence may be divided into multiple sections and each section may be padded in the same padding manner. Latter on, the transmitter transmits the padded code sequence to a receiver via an air interface. Upon receiving the padded code sequence via the air interface, the receiver may detect the padded sequence according to its structure, e.g. differential detection.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. Provisional Application No.61/218,685, filed on Jun. 22, 2009, the entirety of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to wireless communication technologies,and more particularly, to code sequence generation systems and methodsfor providing a padded code sequence.

2. Description of the Related Art

For a wireless communication environment utilizing OrthogonalFrequency-Division Multiplexing (OFDM) technology. Transmission data iscarried in a plurality of orthogonal sub-carriers. For example, thetransmission data is divided into multiple groups and each group ismapped into one modulation symbol, and these modulation symbols arefurther placed on these sub-carriers. Subsequently, transmitter performsFast Fourier Transform (FFT) and produces time-domain samples, and thenthe transmitter performs digital to analog (D/A) conversion andgenerates time-domain continuous waveform. Then the transmitter performsup-conversion on the produced time-domain waveform to a carrier. Singlecarrier OFDM (SC-OFDM) is a similar technology to the OFDM. Thetransmitter performs FFT on the modulation symbols, and allocates thetransformed samples on frequency domain. Transmitter continues withperforming inversed FFT (IFFT), and then performing the D/A conversionand up-covert to a carrier. The OFDM technology is widely adopted in alarge number of wireless communication standards, such as IEEE802.11a/g, the Ultra-WideBand (UWB), the Worldwide Interoperability forMicrowave Access (WiMAX), 3GPP Long Term Evolution (LTE), etc. SC-OFDMis applied in the uplink for the 3GPP LTE.

Zadoff-Chu code features low peak to average power ratio, zerocross-correlation, low complexity receiver, etc. The LTE has adoptedthis code in synchronization channel, uplink control channel, etc. Thereare some other codes with similar features such as generalizedchirp-like code, CAZAC sequence. Within a set of Zadoff-Chu code, thecodes are orthogonal and provide excellent detection probability ifmatch detection is used. However, when the differential detection isapplied, this code is not optimal.

BRIEF SUMMARY OF THE INVENTION

Accordingly, embodiments of the invention provide systems and methodsfor code sequence extension over transmission in wireless communicationenvironments. In one aspect of the invention, a transmitter fortransmitting signals to a receiver is provided. The transmittergenerates a padded code sequence comprising a plurality of symbols withthe last symbol being a duplication of the first symbol, and transmitsthe padded code sequence to a receiver via an air interface.

In another aspect of the invention, an OFDM transmitter for transmittingsignals to a receiver is provided. The OFDM transmitter generates apadded Zadoff-Chu code sequence comprising a plurality of symbols for aranging preamble code with the last symbol being a duplication of thefirst symbol, and transmits the padded Zadoff-Chu code sequence to areceiver via an air interface. The transmitted code sequence can be usedfor ranging preamble code or synchronization channel.

In another aspect of the invention, a transmission method for a wirelesscommunication device is provided. The transmission method comprises thesteps of generating a padded code sequence comprising a plurality ofsymbols with the last symbol being a duplication of the first symbol,and transmitting the padded code sequence to a receiver via an airinterface.

In another aspect of the invention, a transmission method for an OFDMwireless communication device is provided. The transmission methodcomprises the steps of generating a padded Zadoff-Chu code sequencecomprising a plurality of symbols for a ranging preamble code with thelast symbol being a duplication of the first symbol, and transmittingthe padded Zadoff-Chu code sequence to a receiver via an air interface.

In another aspect of the invention, a machine-readable storage medium isprovided. The machine-readable storage medium comprises a computerprogram which, when executed, causes a wireless communication device toperform a transmission method. The transmission method comprises thesteps of generating a padded code sequence comprising a plurality ofsymbols with the last symbol being a duplication of the first symbol,and transmitting the padded code sequence to a receiver via an airinterface.

In another aspect of the invention, a machine-readable storage medium isprovided. The machine-readable storage medium comprises a computerprogram which, when executed, causes an OFDM wireless communicationdevice to perform a transmission method. The transmission methodcomprises the steps of generating a padded Zadoff-Chu code sequencecomprising a plurality of symbols for a ranging preamble code with thelast symbol being a duplication of the first symbol, and transmittingthe padded Zadoff-Chu code sequence to a receiver via an air interface.

Other aspects and features of the invention will become apparent tothose with ordinary skill in the art upon review of the followingdescriptions of specific embodiments of the transmitter, the OFDMtransmitter, the transmission methods, and the machine-readable storagemediums for code sequence extension over transmission in wirelesscommunication environments.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the invention;

FIGS. 2A to 2C are block diagrams illustrating padded Zadoff-Chu codesequences on frequency domain according to an embodiment of theinvention;

FIG. 3 is a block diagram illustrating duplications of a paddedZadoff-Chu code sequence on time domain according to an embodiment ofthe invention;

FIG. 4 is a block diagram illustrating a padded Zadoff-Chu code sequenceon both frequency and time domains according to an embodiment of theinvention;

FIG. 5 is a block diagram illustrating duplications of a paddedZadoff-Chu code sequence on time domain according to an embodiment ofthe invention;

FIG. 6 is a block diagram illustrating duplications of padded Zadoff-Chucode sequences with distributed structure on frequency domain accordingto an embodiment of the invention;

FIG. 7 is a block diagram illustrating multiple padded Zadoff-Chu codesequences with distributed structure according on frequency domain to anembodiment of the invention;

FIG. 8 is a block diagram illustrating a padded Zadoff-Chu code sequencewith distributed structure on frequency domain according to anembodiment of the invention;

FIGS. 9A to 9B are block diagrams illustrating duplications of a paddedZadoff-Chu code sequence in relation to 2 antennas on the frequencydomain according to an embodiment of the invention;

FIG. 10 is a block diagram illustrating a padded Zadoff-Chu codesequence with cyclical shifts for Ranging Preamble (RP) codes accordingto an embodiment of the invention; and

FIG. 11 is a flow chart illustrating a transmission method with codesequence extension according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings represent the same or similar elementsunless otherwise represented. The implementations set forth in thefollowing description of exemplary embodiments consistent with thepresent invention do not represent all implementations consistent withthe invention. Instead, they are merely examples of systems and methodsconsistent with aspects related to the invention as recited in theappended claims.

The proposed method proposed a padding method to Zadoff-Chu codesequence to enhance the code property. After the padding, the Zadoff-Chucode sequence may obtain extra code property, and this code propertyprovides zero cross-correlation after differential operation. FIG. 1 isa block diagram illustrating a wireless communication system accordingto an embodiment of the invention. In the wireless communication system100, a transmitter 110 and a receiver 120 are provided for wirelesscommunications therebetween via the air interface. The transmitter 110generates a padded code sequence comprising a plurality of symbols withthe last symbol being a duplication of the first symbol, to maintainorthogonality of the code sequence in the differential domain.Subsequently, the transmitter 110 transmits the padded code sequence tothe receiver 120 via the air interface. Upon receiving the padded codesequence via the air interface, the receiver 120 may performdifferential detection to detect the padded code sequence. Note that thetransmission between the transmitter 110 and the receiver 120 mayutilize the OFDM technology or the Single Carrier-OFDM (SC-OFDM)technology, and the code sequence may be a Zadoff-Chu code sequence, aGeneralized Chirp-Like (GCL) code sequence, or a Constant Amplitude ZeroAutoCorrelation (CAZAC) code sequence. In order to give clear examples,the following embodiments use Zadoff-Chu code sequences for detaileddescriptions, but the invention is not limited thereto.

FIGS. 2A to 2C are block diagrams illustrating padded Zadoff-Chu codesequences on frequency domain according to an embodiment of theinvention. In this embodiment, the original codeword to be transmittedis a Zadoff-Chu code sequence comprising a plurality of symbols denotedas s₁ to s_(N). The transmitter 110 duplicates the first symbol s₁ andcyclically pads the duplicated symbol to the end of the Zadoff-Chu codesequence. Specifically, each symbol of the padded Zadoff-Chu codesequence is carried on a sub-carrier corresponding to a respective radiofrequency selected in an increasing order on the frequency domain, asshown in FIG. 2A; while in other embodiments, the corresponding radiofrequencies may be selected in a decreasing order on the frequencydomain, as shown in FIG. 2B. In other embodiments, the symbols of thepadded Zadoff-Chu code sequence may be allocated in a circular shiftorder. That is, the padded Zadoff-Chu code sequence may be placed,starting with the (m+1)-th symbol to the N-th symbol and continuing withthe first symbol to the m-th symbol, as shown in FIG. 2C, wherein m maybe any number larger than zero and not greater than N. In this figure,s_(m) equals to s_(1+(m mod N)) if m is larger than N, wherein (m mod N)means the remainder of m divided by N.

FIG. 3 is a block diagram illustrating duplications of a paddedZadoff-Chu code sequence on time domain according to an embodiment ofthe invention. Similar to the embodiment of FIG. 2A to 2C, the originalcodeword to be transmitted is a Zadoff-Chu code sequence comprising aplurality of symbols denoted as s₁ to s_(N), and the first symbol s₁ isduplicated and cyclically padded to the end of the Zadoff-Chu codesequence. However, the padded Zadoff-Chu code sequence is transmittednot only during the time period T₁, but also during the time periods T₂and T₃, wherein the time periods T₁ to T₃ are continuously located in anincreasing order in the time domain. That is, the transmitter 110further duplicates the padded Zadoff-Chu code sequence twice andtransmits the duplicated and padded Zadoff-Chu code sequences during thetime period T₂ and T₃, respectively. Specifically, each symbol of thetwo duplicated and padded Zadoff-Chu code sequences may be allocated onthe same sub-carrier as the corresponding symbol of the paddedZadoff-Chu code sequence. In other embodiments, the number ofduplications may be configured to be any number other than two.

FIG. 4 is a block diagram illustrating a padded Zadoff-Chu code sequenceon both frequency and time domains according to an embodiment of theinvention. In this embodiment, the original codeword to be transmittedis a Zadoff-Chu code sequence comprising a plurality of symbols denotedas s₁ to s_(3R). 3R may be specified in advance. Transmitter 110 andreceiver 120 know the number 3R. In other embodiment, the receiver 120may negotiate with the transmitter 110 to acquire the number 3R. Inother embodiment, the receiver 120 may read broadcasting channel toacquire the number. The transmitter 110 subsequently divides theZadoff-Chu code sequence into 3 sections according to the transmissionlength R. That is, the first section comprises R symbols denoted as s₁to s_(R), the second section comprises R symbols denoted as s_(R+1) tos_(2R), and the third section comprises R symbols denoted as s_(2R+1) tos_(3R). Each symbol of one of the sections may be allocated on arespective sub-carrier corresponding to a respective radio frequencyselected in an increasing order from the frequency domain, and eachsection is transmitted in a respective time period continuously selectedfrom the time domain, as shown in FIG. 4. These sections may be alignedin the time domain such that the symbols in the same position of thesections are corresponding to the same sub-carriers. After theZadoff-Chu code sequence is divided and placed in the described order,the transmitter 110 further duplicates and cyclically pads the firstsymbol of the second section, i.e. the symbol s_(R+1), to the end of thefirst section, the first symbol of the third section, i.e. the symbols_(2R+1), to the end of the second section, and the first symbol of thefirst section, i.e. the symbol S₁, to the end of the third section. Inother embodiments, the radio frequencies corresponding to the symbolsmay be selected in a decreasing order from the frequency domain. Notethat the symbol s₁ is padded after the last symbol of Zadoff-Chu codesequence in the last section. If the length of the Zadoff-Chu codesequence is less than 3R, the transmitter 110 may leave the slotscorresponding to the residual sub-carriers in the third section empty orassign zero to the slots corresponding to the residual sub-carriers inthe third section, after the duplications and cyclical padding are done.

FIG. 5 is a block diagram illustrating duplications of a paddedZadoff-Chu code sequence on time domain according to an embodiment ofthe invention. Similar to the embodiment of FIG. 4, the originalcodeword to be transmitted is a Zadoff-Chu code sequence comprising aplurality of symbols denoted as s₁ to s_(3R), and the Zadoff-Chu codesequence is divided into sections and cyclically padded among thesections. However, the transmitter 110 further duplicates the cyclicallypadded Zadoff-Chu code sequence, and transmits the duplication of thecyclically padded Zadoff-Chu code sequence in the subsequent OFDMsymbols, as shown in FIG. 5. Likewise, in the duplication of the paddedZadoff-Chu code sequence, the sections are aligned in the time domainsuch that the symbols in the same position of the sections arecorresponding to the same radio frequency, and the symbol s₁ is paddedafter the last symbol of Zadoff-Chu code sequence in the last section.If the length of the Zadoff-Chu code sequence is less than 3R, thetransmitter 110 may further leave the slots corresponding to theresidual sub-carriers in the third section empty or assign zero to theslots corresponding to the residual sub-carriers in the third section.

It is noted that the embodiments of FIGS. 2A to 2B and FIGS. 3 to 5 maybe applied in the ranging channel or random access channel in the OFDMor SC-OFDM system.

The padded Zadoff-Chu code sequence may by further duplicated in thefrequency domain in the distributed structure. FIG. 6 is a block diagramillustrating duplications of padded Zadoff-Chu code sequences withdistributed structure on frequency domain according to an embodiment ofthe invention. For a Zadoff-Chu code sequence padded and duplicated asdescribed in the embodiment of FIG. 3, the padded Zadoff-Chu codesequence and the duplications of the padded Zadoff-Chu code sequence maybe taken as a transmission block for simplicity, wherein the symbols ineach padded Zadoff-Chu code sequence of the transmission block areallocated on sub-carriers in an increasing order corresponding to theradio frequency range F_(R1). The transmitter 110 may further duplicatethe transmission block, and transmit the duplicated transmission blockin the radio frequency range F_(R2). Specifically, the symbols in eachpadded Zadoff-Chu code sequence of the duplicated transmission block areallocated on sub-carriers in an increasing order corresponding to theradio frequency range F_(R2). In addition, the padded Zadoff-Chu codesequences in each transmission block are transmitted in three subsequenttime periods, i.e., the first padded Zadoff-Chu code sequences of thetransmission blocks are transmitted during the time period T₁, thesecond padded Zadoff-Chu code sequences of the transmission blocks aretransmitted during the time period T₂, and the third padded Zadoff-Chucode sequences of the transmission blocks are transmitted during thetime period T₃.

It is noted that the distributed structure may be applied to rangingcode or random access channel in an OFDM or SC-OFDM system.

FIG. 7 is a block diagram illustrating multiple padded Zadoff-Chu codesequences with distributed structure on frequency domain according to anembodiment of the invention. For the transmissions of multipleZadoff-Chu code sequences, all the Zadoff-Chu code sequences may bepadded as described in the embodiment of FIG. 2A, except that theplacements of the padded Zadoff-Chu code sequences are on both of thefrequency and time domains. That is, the first Zadoff-Chu code sequence,comprising N symbols denoted as s_(1,1) to s_(1,N), is padded withs_(1,1), the second Zadoff-Chu code sequence, comprising N symbolsdenoted as s_(2,1) to s_(2,N), is padded with s_(2,1), and the thirdZadoff-Chu code sequence, comprising N symbols denoted as s_(3,1) tos_(3,N), is padded with s_(3,1), etc. For simplicity, every three paddedZadoff-Chu code sequences may be taken as a transmission block, i.e.,the first transmission block comprises the padded first, second, andthird Zadoff-Chu code sequences, and the second transmission blockcomprises the padded fourth, fifth, and sixth Zadoff-Chu code sequences.Specifically, the symbols in each padded Zadoff-Chu code sequence of thefirst transmission block are allocated on sub-carriers in an increasingorder corresponding to the radio frequency range F_(R1), and the symbolsin each padded Zadoff-Chu code sequence of the second transmission blockare allocated on sub-carriers in an increasing order corresponding tothe radio frequency range F_(R2). In addition, the padded Zadoff-Chucode sequences in each transmission block are transmitted in threesubsequent time periods, i.e., the padded first and fourth Zadoff-Chucode sequences are transmitted during the time period T₁, the paddedsecond and fifth Zadoff-Chu code sequences are transmitted during thetime period T₂, and the padded third and sixth Zadoff-Chu code sequencesare transmitted during the time period T₃.

It is noted that the distributed structure may be applied to rangingcode or random access channel in an OFDM or SC-OFDM system.

FIG. 8 is a block diagram illustrating a padded Zadoff-Chu code sequencewith distributed structure on frequency domain according to anembodiment of the invention. In this embodiment, the length of theZadoff-Chu code sequence is 6R and the Zadoff-Chu code sequence isdivided into 6 sections with R symbols. Regarding the cyclical paddingof symbols in these sections, references may be made to the embodimentof FIG. 4. To further clarify, the transmitter 110 duplicates and padsthe first symbol of the second section, i.e. the symbol s_(R+1) to theend of the first section, the first symbol of the third section, i.e.the symbol s_(2R+1) to the end of the second section, the first symbolof the fourth section, i.e. the symbol s_(3R+1) to the end of the thirdsection. Likewise, the transmitter 110 duplicates and pads the firstsymbol of the fifth section, i.e. the symbol s_(4R+1), to the end of thefourth section, the first symbol of the sixth section, i.e. the symbols_(5R+1), to the end of the fifth section, and lastly, cyclicallyduplicates and pads the first symbol of the first section, i.e. thesymbol s₁, to the end of the sixth section. For simplicity, every threepadded sections of the Zadoff-Chu code sequence may be taken as atransmission block, wherein the symbols in each padded section of thefirst transmission block are allocated on sub-carriers in an increasingorder corresponding to the radio frequency range F_(R1), and the symbolsin each padded section of the second transmission block are allocated onsub-carriers in an increasing order corresponding to the radio frequencyrange F_(R2). In addition, the padded sections of each transmissionblock are transmitted in three subsequent time periods, i.e., the firstpadded sections of the first and second transmission blocks aretransmitted during the time period T₁, the second padded sections of thefirst and second transmission blocks are transmitted during the timeperiod T₂, and the third padded sections of the first and secondtransmission blocks are transmitted during the time period T₃.

It is noted that the distributed structure may be applied to rangingcode or random access channel in an OFDM or SC-OFDM system.

In addition to the ranging channel and random access channel, theembodiments of FIGS. 2A to 2B and FIGS. 3 to 5 may also be applied tothe synchronization channel in the OFDM or SC-OFDM system. If thetransmitter 110 has only one antenna (now shown) coupled therein fortransmitting the code sequences, the embodiments of FIGS. 2A to 2B andFIGS. 3 to 5 may be applied to padding the code sequences as describedabove. Otherwise, if the transmitter 110 has multiple antennas (nowshown) coupled therein for transmitting the code sequence, thetransmitter 110 may further duplicate the padding of the code sequenceson the frequency domain. FIGS. 9A to 9B are block diagrams illustratingduplications of a padded Zadoff-Chu code sequence in relation to 2antennas on the frequency domain according to an embodiment of theinvention. With multiple antennas, the transmitter 110 may transmit, inthe same time period, code sequences in multiple radio frequency ranges.For example, the transmitter 110 may use a first antenna to transmit thepadded Zadoff-Chu code sequence of FIG. 2A in the radio frequency rangeF_(R1), and use a second antenna to transmit the duplication of thepadded Zadoff-Chu code sequence in the radio frequency range F_(R2), asshown in FIG. 9A. Alternatively, the transmitter 110 may use a firstantenna to transmit the padded first section of the Zadoff-Chu codesequence of FIG. 4 in the radio frequency range F_(R1), and use a secondantenna to transmit the padded second section of the Zadoff-Chu codesequence of FIG. 4 in the radio frequency range F_(R2), etc., as shownin FIG. 9B. In other embodiments, the number of antennas coupled in thetransmitter 110 may be more than two.

FIG. 10 is a block diagram illustrating a padded Zadoff-Chu codesequence with cyclic shifts for Ranging Preamble (RP) codes according toan embodiment of the invention. The placement of the symbols in an RPcode are given by the following equation:

${{x_{p}\left( {n,k} \right)} = {\exp\left( {{- j} \cdot {\pi\left( {\frac{r_{p} \cdot \left( {{n \cdot 71} + k} \right) \cdot \left( {{n \cdot 71} + k + 1} \right)}{211} + \frac{2 \cdot k \cdot s_{p} \cdot N_{TCS}}{N_{FFT}}} \right)}} \right)}},{{{where}\mspace{14mu} k} = 0},1,\ldots\mspace{14mu},{{N_{RP} - 1};{n = 0}},1,2$wherein x_(p)(n, k) represents the p-th RP code for the n-th OrthogonalFrequency-Division Multiple Access (OFDMA) symbol, p is the index forthe p-th RP code within a basic unit which is made as the s_(p)-thcyclically shifted sequence from the root index r_(p) of Zadoff-Chu codesequence, N_(RP) represents the length of the RP codes per OFDMA symbol,N_(TCS) represents the unit of time domain cyclical shift per OFDMAsymbol, and N_(FFT) represents the Fast Fourier Transform (FFT) size.For the case where N_(Rp) equals to 72, the placement of the symbols ina padded Zadoff-Chu code sequence may be given as shown in FIG. 10,wherein the Zadoff-Chu code sequence with 211 symbols are divided intothree sections. The equation is extended from the padded Zadoff-Chu codeas follows:

${{x_{p}^{\prime}\left( {n,k} \right)} = {\exp\left( {{- j} \cdot {\pi\left( \frac{r_{p} \cdot \left( {{n \cdot 71} + k} \right) \cdot \left( {{n \cdot 71} + k + 1} \right)}{211} \right)}} \right)}},{{{where}\mspace{14mu} k} = 0},1,\ldots\mspace{14mu},{{N_{RP} - 1};{n = 0}},1,2$

According to the equation, x′_(p)(0,71) is the same as x′_(p)(1,0),x′_(p)(1,71) is the same as x′_(p)(2,0), x′(2,69) is the same asx′_(p)(0,0). Therefore, x_(p)(0,71) is the same as x_(p)(1,0) with

$\exp\left( {{- j} \cdot {\pi\left( \frac{2 \cdot 71 \cdot s_{p} \cdot N_{TCS}}{N_{FFT}} \right)}} \right)$phase rotation, x_(p)(1,71) is the same as x_(p)(2,0) with

$\exp\left( {{- j} \cdot {\pi\left( \frac{2 \cdot 71 \cdot s_{p} \cdot N_{TCS}}{N_{FFT}} \right)}} \right)$phase rotation, and x_(p)(2,69) is the same as x_(p)(0,0) with

$\exp\left( {{- j} \cdot {\pi\left( \frac{2 \cdot 69 \cdot s_{p} \cdot N_{TCS}}{N_{FFT}} \right)}} \right)$phase rotation. Note that the residual slots in the end of the paddedthird section are further padded with the duplication of the second andthird symbols of the first section, i.e., the x_(p)(0,1) and x_(p)(0,2),according to the same cyclical padding manner.

FIG. 11 is a flow chart illustrating a transmission method with codesequence extension according to an embodiment of the invention. Thetransmission method may be applied in a wireless communication device,such as the transmitter 110, for code sequence transmission to areceiver via the air interface. The wireless communication device andthe receiver may be in compliance with the OFDM technology or theSC-OFDM technology. To begin, the wireless communication devicegenerates a padded code sequence comprising a plurality of symbols withthe last symbol being a duplication of the first symbol (step S1101). Tobe more specific, the wireless communication device may first generatean original code sequence. Subsequently, the wireless communicationdevice extends the original code sequence with cyclical padding aduplication of the first symbol to the end of the original codesequence. After generating the padded code sequence, the wirelesscommunication device further transmits the padded code sequence to thereceiver via the air interface (step 1102). Thus, the transmission ofthe code sequence between the wireless communication device and thereceiver is achieved successfully. The padded code sequence may becarried out in several embodiments as described above. For example, inthe case where the padded code sequence is applied to the rangingchannel or the random access channel in an OFDM or a SC-OFDM system, thefirst symbol of the original code sequence may be duplicated andcyclically padded to the end of the original code sequence, as shown inFIG. 2A, 2B, or 2C, and even more, the padded code sequence may befurther duplicated in the time domain, as shown in FIG. 3.Alternatively, the original code sequence may be divided into sectionsand the first symbol of each section is duplicated and cyclically paddedto the end of the previous section, as shown in FIG. 4, and even more,the padded code sequence may be further duplicated on the time domain,as shown in FIG. 5. In another embodiment, for the case where thedistributed structure is employed for the ranging channel or the randomaccess channel, the padding rule of the padded code sequence asdescribed above with respect to FIGS. 2A to 2C may be used for eachdistributed transmission block, as shown in FIG. 6A, or the padding ruleas described above with respect to FIG. 4 may be used, as shown in FIG.6C. Specifically, when multiple original code sequences are provided,the padding rule as described above with respect to FIGS. 2A to 2C mayalso be used for each original code sequence and the padded originalcode sequences are aligned on the time domain for each distributedtransmission block. Yet in other embodiments, for the case where thepadded code sequence is applied to the synchronization channel withmultiple antennas, the code sequence may be padded, duplicated, andtransmitted using the multiple antennas according to the padding rule asdescribed above with respect to FIGS. 2A to 2C with a respectiveantenna, as shown in FIG. 9A, or may be divided, padded, and transmittedaccording to the padding rule as described above with respect to FIG. 4,as shown in FIG. 9B. Note that the code sequence may be a Zadoff-Chucode sequence, a GCL code sequence, or a CAZAC code sequence.

Take the Zadoff-Chu code sequence for an RP code for example. TheZadoff-Chu code sequence is a complex-valued mathematical sequence, andwhen applied to radio signals, gives rise to an electromagnetic signalof constant amplitude. Specifically, the cyclically padded version ofthe code sequence as proposed in the invention exhibits a usefulproperty that the symbols therein do not cross-correlate with each other(i.e., each symbol remains orthogonal to one another), so that the radiosignals may be recovered at the receiver end. Regarding the detaileddescription of the cyclically shifting rule for an RP code, referencesmay be made to FIG. 10, where the Zadoff-Chu code sequence for the RPcode is divided into sections, and then duplicated and cyclicallyshifted according to the padding rule as described above with respect toFIG. 4. Note that if there are residual slots in the end of the lastsection, the residual slots may be padded with the duplication of thesymbols following the padding symbol, or may be padded with zero-valuedsymbols. In other embodiments, the cyclically shifting rule for the RPcode may be used as described above with respect to FIGS. 2A to 2C, 3,5, 6A to 6C, and 9A to 9B.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. Those who are skilled in this technology can still makevarious alterations and modifications without departing from the scopeand spirit of this invention. For example, the wireless communicationdevice, such as the transmitter 110, and the receiver may becommunicating with each other according to any wireless communicationstandards adopting the OFDM technology, the SC-OFDM technology, or otherevolutionary technologies of the OFDM technology family, including theWLAN, the UWB, the WiMAX, the Wireless Broadband (WiBro), and the LTE,etc. Therefore, the scope of the invention shall be defined andprotected by the following claims and their equivalents.

What is claimed is:
 1. A transmitter for transmitting signals to areceiver, wherein the transmitter is configured to generate a paddedcode sequence comprising a plurality of symbols with the last symbolbeing a duplication of the first symbol, determine a transmission lengthand divide the padded code sequence into at least two sections accordingto the transmission length, and transmit said sections of the paddedcode sequence to the receiver via an air interface, wherein the lastsymbol of each of said sections is the duplication of the first symbolin the next section, except that the last symbol of the last section isthe duplication of the first symbol of the first section, wherein, inresponse to the last section being shorter than the transmission length,the last section is padded with a number of continuous symbolssubsequent to the first symbol of the first section, causing the lastsection equal to the transmission length.
 2. The transmitter of claim 1,wherein the receiver further receives the padded code sequence via theair interface, and performs differential detection on the padded codesequence.
 3. The transmitter of claim 1, wherein the padded codesequence is transmitted with the symbols therein respectivelycorresponding to a plurality of first sub-carriers.
 4. The transmitterof claim 3, wherein the first sub-carriers are selected in acontinuously increasing order or a continuously decreasing order from afrequency domain.
 5. The transmitter of claim 3, wherein the padded codesequence is transmitted using a first antenna in a time period, and thetransmitter is further configured to duplicate the padded code sequenceand transmit the duplicated padded code sequence with the symbolstherein respectively corresponding to a plurality of second sub-carriersusing a second antenna in the time period.
 6. The transmitter of claim5, wherein the first sub-carriers and the second sub-carriers areselected in a continuously increasing order or a continuously decreasingorder from a frequency domain, respectively.
 7. The transmitter of claim1, wherein the padded code sequence is transmitted with the symbolstherein corresponding to a plurality of first sub-carriers in a firsttime period, and the transmitter further duplicates the padded codesequence and transmits the duplicated and padded code sequence with thesymbols therein corresponding to the first sub-carriers in a second timeperiod subsequent to the first time period.
 8. The transmitter of claim7, wherein the first sub-carriers are selected in a continuouslyincreasing order or a continuously decreasing order from a frequencydomain.
 9. The transmitter of claim 7, further configured to duplicatethe padded code sequence and transmit the duplicated and padded codesequence with the symbols therein corresponding to a plurality of secondsub-carriers in the first time period and the second time period. 10.The transmitter of claim 9, wherein the first sub-carriers and thesecond sub-carriers are selected in a continuously increasing order or acontinuously decreasing order from a frequency domain.
 11. Thetransmitter of claim 1, wherein the first section of the padded codesequence is transmitted with the symbols therein corresponding to aplurality of first sub-carriers in a first time period, and the secondsection of the padded code sequence is transmitted with the symbolstherein corresponding to the first sub-carriers in a second time periodsubsequent to the first time period.
 12. The transmitter of claim 11,further configured to duplicate the first section and the second sectionof the padded code sequence, and transmit the duplicated first sectionand second section of the padded code sequence with the symbols thereincorresponding to the first sub-carriers in a third time periodsubsequent to the second time period and a fourth time period subsequentto the third time period, respectively.
 13. The transmitter of claim 11,wherein the first sub-carriers are selected in a continuously increasingorder or a continuously decreasing order from a frequency domain. 14.The transmitter of claim 1, wherein the first section of the padded codesequence is transmitted with the symbols therein respectivelycorresponding to a plurality of first sub-carriers in a time period, andthe second section of the padded code sequence is transmitted with thesymbols therein respectively corresponding to a plurality of secondsub-carriers in the time period.
 15. The transmitter of claim 14,wherein the first sub-carriers and the second sub-carriers are selectedin a continuously increasing order or a continuously decreasing orderfrom a frequency domain, respectively, the second sub-carriers arelatter than the first sub-carriers in the frequency domain.
 16. Thetransmitter of claim 15, wherein the first section of the padded codesequence is transmitted using a first antenna, and the second section ofthe padded code sequence is transmitted using a second antenna.
 17. Thetransmitter of claim 1, wherein the padded code sequence is transmittedin a ranging channel, a random access channel, or a synchronizationchannel of an Orthogonal Frequency-Division Multiplexing (OFDM)environment or a Synchronous Coherent-OFDM (SC-OFDM) environment. 18.The transmitter of claim 1, wherein the padded code sequence isgenerated from a Zadoff-Chu code sequence, a Generalized Chirp-Like(GCL) code sequence, or a Constant Amplitude Zero AutoCorrelation(CAZAC) code sequence.
 19. A transmission method for a wirelesscommunication device, comprising: generating a padded code sequencecomprising a plurality of symbols with the last symbol being aduplication of the first symbol; determining a transmission length anddividing the padded code sequence into at least two sections accordingto the transmission length, wherein the last symbol of each of saidsections is the duplication of the first symbol in the next section,except that the last symbol of the last section is the duplication ofthe first symbol of the first section; and transmitting said sections ofthe padded code sequence to a receiver via an air interface, wherein, inresponse to the last section being shorter than the transmission length,the last section is padded with a number of continuous symbolssubsequent to the first symbol of the first section, causing the lastsection equal to the transmission length.
 20. The transmission method ofclaim 19, wherein the receiver further receives the padded code sequencevia the air interface, and performs differential detection on the paddedcode sequence.
 21. The transmission method of claim 19, wherein thepadded code sequence is transmitted with the symbols thereinrespectively corresponding to a plurality of first sub-carriers.
 22. Thetransmission method of claim 21, wherein the first sub-carriers areselected in a continuously increasing order or a continuously decreasingorder from a frequency domain.
 23. The transmission method of claim 21,wherein the padded code sequence is transmitted using a first antenna ina time period, and the transmission method further comprises duplicatingthe padded code sequence and transmitting the duplicated and padded codesequence with the symbols therein respectively corresponding to aplurality of second sub-carriers using a second antenna in the timeperiod.
 24. The transmission method of claim 23, wherein the firstsub-carriers and the second sub-carriers are selected in a continuouslyincreasing order or a continuously decreasing order from a frequencydomain, respectively.
 25. The transmission method of claim 19, whereinthe padded code sequence is transmitted in a first time period with thesymbols therein corresponding to a plurality of first sub-carriersselected in a continuously increasing order or a continuously decreasingorder from a frequency domain, and the transmission method furthercomprises duplicating the padded code sequence and transmitting theduplicated and padded code sequence with the symbols thereincorresponding to the first radio frequencies in a second time periodsubsequent to the first time period.
 26. The transmission method ofclaim 25, further comprising duplicating the padded code sequence andtransmitting the duplicated and padded code sequence in the first timeperiod and the second time period with the symbols therein correspondingto a plurality of second sub-carriers selected in the continuouslyincreasing order or the continuously decreasing order from the frequencydomain.
 27. The transmission method of claim 19, wherein the firstsection of the padded code sequence is transmitted in a first timeperiod with the symbols therein corresponding to a plurality of firstsub-carriers selected in a continuously increasing order or acontinuously decreasing order from a frequency domain, and the secondsection of the padded code sequence is transmitted in a second timeperiod subsequent to the first time period with the symbols thereincorresponding to the first sub-carriers.
 28. The transmission method ofclaim 27, further comprising duplicating the first section and thesecond section of the padded code sequence, and transmitting theduplicated first section and second section of the padded code sequencewith the symbols therein corresponding to the first sub-carriers in athird time period subsequent to the second time period and a fourth timeperiod subsequent to the third time period, respectively.
 29. Thetransmission method of claim 19, wherein the first section of the paddedcode sequence is transmitted with the symbols therein respectivelycorresponding to a plurality of first sub-carriers selected in acontinuously increasing order or a continuously decreasing order from afrequency domain in a time period, and the second section of the paddedcode sequence is transmitted with the symbols therein respectivelycorresponding to a plurality of second sub-carriers selected in thecontinuously increasing order or the continuously decreasing order fromthe frequency domain in the time period.
 30. The transmission method ofclaim 29, wherein the first section of the padded code sequence istransmitted using a first antenna, and the second section of the paddedcode sequence is transmitted using a second antenna.
 31. Thetransmission method of claim 19, wherein the padded code sequence istransmitted in a ranging channel, a random access channel, or asynchronization channel of an Orthogonal Frequency-Division Multiplexing(OFDM) environment or a Synchronous Coherent-OFDM (SC-OFDM) environment.32. The transmission method of claim 19, wherein the padded codesequence is generated from a Zadoff-Chu code sequence, a GeneralizedChirp-Like (GCL) code sequence, or a Constant Amplitude ZeroAutoCorrelation (CAZAC) code sequence.
 33. A non-transitorymachine-readable storage medium comprising a computer program, whenexecuted, causes a wireless communication device to perform atransmission method, wherein the transmission method comprises:generating a padded code sequence comprising a plurality of symbols withthe last symbol being a duplication of the first symbol; determining atransmission length and dividing the padded code sequence into at leasttwo sections according to the transmission length, wherein the lastsymbol of each of said sections is the duplication of the first symbolin the next section, except that the last symbol of the last section isthe duplication of the first symbol of the first section; andtransmitting said sections of the padded code sequence to a receiver viaan air interface, wherein, in response to the last section being shorterthan the transmission length, the last section is padded with a numberof continuous symbols subsequent to the first symbol of the firstsection, causing the last section equal to the transmission length. 34.The non-transitory machine-readable storage medium of claim 33, whereinthe receiver further receives the padded code sequence via the airinterface, and performs differential detection on the padded codesequence.
 35. The non-transitory machine-readable storage medium ofclaim 33, wherein the padded code sequence is transmitted with thesymbols therein respectively corresponding to a plurality of firstsub-carriers.
 36. The non-transitory machine-readable storage medium ofclaim 33, wherein the first sub-carriers are selected in a continuouslyincreasing order or a continuously decreasing order from a frequencydomain.
 37. The non-transitory machine-readable storage medium of claim35, wherein the padded code sequence is transmitted using a firstantenna in a time period, and the transmission method further comprisesduplicating the padded code sequence and transmitting the duplicated andpadded code sequence with the symbols therein respectively correspondingto a plurality of second sub-carriers using a second antenna in the timeperiod.
 38. The non-transitory machine-readable storage medium of claim37, wherein the first sub-carriers and the second sub-carriers areselected in a continuously increasing order or a continuously decreasingorder from a frequency domain.
 39. The non-transitory machine-readablestorage medium of claim 33, wherein the padded code sequence istransmitted in a first time period with the symbols thereincorresponding to a plurality of first sub-carriers selected in acontinuously increasing order or a continuously decreasing order from afrequency domain, and the transmission method further comprisesduplicating the padded code sequence and transmitting the duplicated andpadded code sequence with the symbols therein corresponding to the firstsub-carriers in a second time period subsequent to the first timeperiod.
 40. The non-transitory machine-readable storage medium of claim39, wherein the transmission method further comprises duplicating thepadded code sequence and transmitting the duplicated and padded codesequence in the first time period and the second time period with thesymbols therein corresponding to a plurality of second sub-carriersselected in the continuously increasing order or the continuouslydecreasing order from the frequency domain.
 41. The non-transitorymachine-readable storage medium of claim 33, wherein the first sectionof the padded code sequence is transmitted in a first time period withthe symbols therein corresponding to a plurality of first sub-carriersselected in a continuously increasing order or a continuously decreasingorder from a frequency domain, and the second section of the padded codesequence is transmitted in a second time period subsequent to the firsttime period with the symbols therein corresponding to the firstsub-carriers.
 42. The non-transitory machine-readable storage medium ofclaim 41, wherein the transmission method further comprises duplicatingthe first section and the second section of the padded code sequence,and transmitting the duplicated first section and second section of thepadded code sequence with the symbols therein corresponding to the firstsub-carriers in a third time period subsequent to the second time periodand a fourth time period subsequent to the third time period,respectively.
 43. The non-transitory machine-readable storage medium ofclaim 33, wherein the first section of the padded code sequence istransmitted with the symbols therein respectively corresponding to aplurality of first sub-carriers selected in a continuously increasingorder or a continuously decreasing order from a frequency domain in atime period, the second section of the padded code sequence istransmitted with the symbols therein respectively corresponding to aplurality of second sub-carriers selected in the continuously increasingorder or the continuously decreasing order from the frequency domain inthe time period, and the second sub-carriers are latter than the firstsub-carriers in the frequency domain.
 44. The non-transitorymachine-readable storage medium of claim 43, wherein the first sectionof the padded code sequence is transmitted using a first antenna, andthe second section of the padded code sequence is transmitted using asecond antenna.
 45. The non-transitory machine-readable storage mediumof claim 33, wherein the padded code sequence is transmitted in aranging channel, a random access channel, or a synchronization channelof an Orthogonal Frequency-Division Multiplexing (OFDM) environment or aSynchronous Coherent-OFDM (SC-OFDM) environment.
 46. The non-transitorymachine-readable storage medium of claim 33, wherein the padded codesequence is generated from a Zadoff-Chu code sequence, a GeneralizedChirp-Like (GCL) code sequence, or a Constant Amplitude ZeroAutoCorrelation (CAZAC) code sequence.